This invention relates to a package of photosensitive planographic printing plates and a photosensitive planographic printing plate, wherein slippage of the photosensitive planographic printing plate(s) is inhibited.
Heretofore, various techniques have been disclosed with respect to packages of photosensitive planographic printing plates. For example, a technique of packaging photosensitive planographic printing plates wherein a photosensitive planographic printing plate and a protection paper are superposed alternately for the purpose of facilitating cutting of the photosensitive planographic printing plates and protecting the surface of the photosensitive layer from abrasion.
In the case of packaging photosensitive printing plate for planography or letterpress printing using metal plate, such as aluminum, iron or zinc, as the support, a stack of several to tens sheets of the photosensitive printing plate is packaged, in general, as a unit package. In this case, the surface of the photosensitive layer was occasionally damaged by the friction between the photosensitive printing plates in a stacked state. Moreover, a guillotine knife which tends to be damaged upon cutting a stack of tens sheets of the photosensitive printing plate having a metal support without protection paper into a designed size by the guillotine cutter. As a result, the cut face of the photosensitive planographic printing plate did become not a mirror face but a nicked face, and the guillotine knife must be changed.
Therefore, the above technique of packaging photosensitive planographic printing plates with superposing a photosensitive planographic printing plate and a protection paper alternately was developed so as to protect the surface of the photosensitive layer from abrasion and so as not to damage the guillotine knife resulting in the increase of cutting times. The protection paper is softer than the photosensitive layer, and is required to have good adhesiveness to and nevertheless easy separability from the photosensitive printing plate and small frictional electrification, as well as protection of the photosensitive layer and the improvement in cutting ability.
Examples of the protection paper are disclosed in Japanese Patent KOKAI Nos. 55-118041, Japanese Patent KOKOKU No. 61-19025, Japanese Patent KOKAI No. 57-99647 and U.S. Pat. No. 4,403,030 which corresponds to and they were developed for the improvement in the cutting ability, the adhesiveness and the separability.
Incidentally, slippage occasionally occurs in the stack of the photosensitive planographic printing plates and protection papers superposed alternately during transport or the like. However, the problem of the slippage, especially a means for resolving the slippage and abrasion of photosensitive layer simultaneously, was not considered in the above conventional techniques at all, and any effective countermeasure was not known.
An object of the invention is to provide a package of photosensitive planographic printing plates comprising a stack of the photosensitive planographic printing plates and protection papers superposed alternately, wherein the slippage between the photosensitive planographic printing plate and the protection paper rarely occurs and the abrasion of the surface of the photosensitive layer also rarely occurs.
Another object of the invention is to provide a photosensitive planographic printing plate which is resistant to slip on a protection paper and to abrasion of its photosensitive layer.
The inventors investigated in order to achieve the above objects, and found that it is effective for resolving the above coexisting problems that the coefficient of static friction between the photosensitive planographic printing plate and the protection paper is in a definite value or more.
Thus, the present invention provides a package of photosensitive planographic printing plates which comprises a stack of the photosensitive planographic printing plates between each of which a protection paper is interposed, wherein the coefficient of static friction between the surface of the photosensitive layer of the photosensitive planographic printing plate and the surface of the protection paper is 0.3 or more.
The present invention also provides a package of photosensitive planographic printing plates which comprises a stack of the photosensitive planographic printing plates between each of which a protection paper is interposed, wherein the coefficient of static friction between the surface opposite to the photosensitive layer of the photosensitive planographic printing plate and the surface of the protection paper is 0.3 or more.
The inventors also found that, as a means for resolving the above coexisting problems, it is effective to provide convexes on the surface of the photosensitive layer and to allow the reverse surface to have a definite surface roughness or more.
Thus, the present invention also provides a photosensitive planographic printing plate which comprises the photosensitive layer of which the surface is provided with convexes having a mean height of 2 xcexcm or more a density of 100 convexes/cm2 or more, and the surface opposite to the photosensitive layer having a mean surface roughness of 0.15 or more.